Do you feel frustrated in your boat? Does sailing fail to bring the satisfaction that it used to? Has the sensual pleasure of yachting paled to a former shadow of its glorious past? Is there something missing? Boat speed? Boat speed is what you get from tuning or, conversely, tuning is how you make your existing boat go faster. So many articles and books have been published on tuning that anyone ought to be able to tune a boat.
The effect of boat speed on sailors is intoxicating. Racing becomes a doddle. Tactics fall into place naturally and the crew's ego travels in a large cloud above the burgee. Every situation is faced with confidence and a dominating ability to escape and continue to the head of the fleet. On the days when the boat is the wrong shape or the rig will not behave, when the boat speed has evaporated the intoxication becomes more like a hangover. Tactical situations invariably lead to an even worse position and the crew's spirits are somewhere about the level of the water in the bilge. Racing let alone winning, is a struggle.
Tuning is about getting many parts of the boat working in harmony. It is the combination of mast stiffness, rig tension, spreaders, sail shape, centre board position & section and rudder (to name but a few) that need to be set up to match each other. With so many variables (and we haven't even got to the fickleness of the wind yet) it should come as no surprise that tuning is an iterative process. Whilst the coarse rig set up can be achieved fairly quickly, it can take a season to get it perfected as you need to sail in a fleet in all conditions from zephyr light breezes to honking gales.
The ability to tune and change the boat is one of the best features of the National 12. So the best plan is to read this guide, get a basic set up then go sailing. Make notes on the conditions and your performance, analyse the performance then make some changes. Then keep on iterating until it feels right.
There are many books on how sails work and how to get the most out of a boat in general. This guide is written to describe some of the subtleties of 'getting the most' out of a National 12.